Carbon Electrode Devices for Use with Liquids and Associated Methods

ABSTRACT

Electrode devices and systems for use in liquid environments, including associated methods are provided. In one aspect, for example, an electrode device for use in a liquid environment can include a proton exchange membrane having a first side and a second side, a first electrode including a carbon material, where the first electrode is positioned at the first side of the proton exchange membrane, and a second electrode including a carbon material, where the second electrode positioned at the second side of the proton exchange membrane opposite the first electrode. The proton exchange membrane spaces the first electrode and the second electrode at a distance of less than or equal to about 100 microns apart.

PRIORITY DATA

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/636,857, filed on Apr. 23, 2012, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Numerous applications utilize electrically conductive electrodes in a liquid, including liquid purification, ozone and hydrogen generation, and other electrolytic processes. Many conventional electrodes, however, exhibit inefficient functionality in a liquid due to various limitations. For example, metal electrodes tend to break down during use due to the electrolytic action of the process in a liquid such as water. This problem is compounded in more corrosive liquids as the liquid chemically breaks down the metal surface of the electrode. Coatings can be utilized to impede such electrolytic and corrosive breakdown, however such coatings generally are made from a material having a low conductivity, and thus further reduce the effectiveness of the conventional electrode.

SUMMARY OF THE INVENTION

The present disclosure provides electrode devices and systems for use in liquid environments, including associated methods. In one aspect, for example, an electrode device for use in a liquid environment is provided. Such a device can include a proton exchange membrane having a first side and a second side, a first electrode including a carbon material, where the first electrode is positioned at the first side of the proton exchange membrane, and a second electrode including a carbon material, where the second electrode positioned at the second side of the proton exchange membrane opposite the first electrode. The proton exchange membrane spaces the first electrode and the second electrode at a distance of less than or equal to about 100 microns apart. In another aspect, the proton exchange membrane spaces the first electrode and the second electrode at a distance of less than or equal to about 50 microns apart.

Various materials are contemplated for use as the first and/or second electrode. In one aspect, the first and/or second electrode can include a porous layer of DLC, a DLC-coated carbon cloth, a B-doped SiC powder, a porous layer of B-doped SiC, a B-doped SiC-coated carbon cloth, and the like, including a combination thereof. In one specific aspect, the first and/or second electrode can include a DLC-coated carbon cloth. In another specific aspect, the first and/or second electrode can include a porous layer of DLC material. Any of the DLC materials utilized can be either doped or undoped. In one aspect, the DLC is doped with N. In another aspect, the DLC can be a conductive DLC material having an sp3 bonded carbon content from about 20 atom % to about 80 atom % and an sp2 bonded carbon content from about 20 atom % to about 80 atom %. In yet another aspect, at least one of the first electrode or the second electrode includes a B-doped SiC powder.

The present disclosure additionally provides systems for ionizing a liquid. In one aspect, for example, one such system provides a liquid containment vessel having a first chamber and a second chamber, where the first chamber and the second chamber are continuous, and a proton exchange membrane having a first side facing the first chamber and a second side facing the second chamber, where the proton exchange membrane is positioned within the liquid containment vessel to separate the first chamber and the second chamber. The system can also include a first electrode including a carbon material, where the first electrode is positioned at the first side of the proton exchange membrane, and a second electrode including a carbon material, where the second electrode is positioned at the second side of the proton exchange membrane opposite the first electrode. The proton exchange membrane spaces the first electrode and the second electrode at a distance of less than or equal to about 100 microns apart. The system additionally includes a first liquid input coupled to the liquid containment vessel and operable to deliver a liquid into the first chamber, a first liquid output coupled to the liquid containment vessel and operable to remove liquid from the first chamber, a second liquid input coupled to the liquid containment vessel and operable to deliver a liquid into the second chamber, and a second liquid output coupled to the liquid containment vessel and operable to remove liquid from the second chamber. The system can further include an electrical power source electrically coupled between the first electrode and the second electrode.

The present disclosure additionally provides methods for ionizing a liquid. In one aspect, relating to the system described above for example, one such method can include activating the power source to drive a current from the second electrode to the first electrode thus charging the first electrode as an anode and the second electrode as a cathode, delivering a working liquid through the first liquid input into the first chamber, and delivering a carrier liquid through the second liquid input into the second chamber. The method can also include ionizing the working liquid to generate protons therefrom such that the generated protons migrate across the proton exchange membrane toward the cathode and into the carrier liquid in the second chamber, and removing the carrier liquid from the second liquid output. In one specific aspect, the working liquid is water and ionizing the water generates ozone at the anode. In yet another aspect, the ozone is removed from the first chamber with the water by the first liquid output.

There has thus been outlined, rather broadly, the more important features of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from the following detailed description of the invention, taken with the accompanying drawings and claims, or may be learned by the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a liquid electrode device in accordance with one aspect of the present disclosure.

FIG. 2 shows a cross-sectional view of a liquid electrode device in accordance with yet another aspect of the present invention.

FIG. 3 shows a method of ionizing a liquid in accordance with a further aspect of the present invention.

The drawings will be described further in connection with the following detailed description. Further, these drawings are not necessarily to scale and are by way of illustration only such that dimensions and geometries can vary from those illustrated.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular structures, process steps, or materials disclosed herein, but is extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

It must be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “the layer” includes one or more of such layers, reference to “an additive” includes reference to one or more of such materials, and reference to “a cathodic arc technique” includes reference to one or more of such techniques.

DEFINITIONS

In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set forth below.

As used herein, “electrode” refers to a conductor used to make electrical contact between at least two points in a circuit.

As used herein, “sp³ bonded carbon” refers to carbon atoms bonded to neighboring carbon atoms in a crystal structure substantially corresponding to the diamond isotope of carbon (i.e. pure sp³ bonding), and further encompasses carbon atoms arranged in a distorted tetrahedral coordination sp³ bonding, such as amorphous diamond and diamond-like carbon.

As used herein, “sp² bonded carbon” refers to carbon atoms bonded to neighboring carbon atoms in a crystal structure substantially corresponding to the graphitic isotope of carbon.

As used herein, “diamond” refers to a crystalline structure of carbon atoms bonded to other carbon atoms in a lattice of tetrahedral coordination known as sp³ bonding. Specifically, each carbon atom is surrounded by and bonded to four other carbon atoms, each located on the tip of a regular tetrahedron. Further, the bond length between any two carbon atoms is 1.54 angstroms at ambient temperature conditions, and the angle between any two bonds is 109 degrees, 28 minutes, and 16 seconds although experimental results may vary slightly. The structure and nature of diamond, including many of its physical and electrical properties are well known in the art.

As used herein, “distorted tetrahedral coordination” refers to a tetrahedral bonding configuration of carbon atoms that is irregular, or has deviated from the normal tetrahedron configuration of diamond as described above. Such distortion generally results in lengthening of some bonds and shortening of others, as well as the variation of the bond angles between the bonds. Additionally, the distortion of the tetrahedron alters the characteristics and properties of the carbon to effectively lie between the characteristics of carbon bonded in sp³ configuration (i.e. diamond) and carbon bonded n sp² configuration (i.e. graphite). One example of material having carbon atoms bonded in distorted tetrahedral bonding is amorphous diamond. It will be understood that many possible distorted tetrahedral configurations exist and a wide variety of distorted configurations are generally present in amorphous diamond.

As used herein, “diamond-like carbon” refers to a carbonaceous material having carbon atoms as the majority element, with a substantial amount of such carbon atoms bonded in distorted tetrahedral coordination. Diamond-like carbon (DLC) can typically be formed by PVD processes, although CVD or other processes could be used such as vapor deposition processes. Notably, a variety of other elements can be included in the DLC material as either impurities, or as dopants, including without limitation, hydrogen, sulfur, phosphorous, boron, nitrogen, silicon, tungsten, etc.

As used herein, “amorphous diamond” refers to a type of diamond-like carbon having carbon atoms as the majority element, with a substantial amount of such carbon atoms bonded in distorted tetrahedral coordination. In one aspect, the amount of carbon in the amorphous diamond can be at least about 90%, with at least about 20% of such carbon being bonded in distorted tetrahedral coordination. Amorphous diamond also has a higher atomic density than that of diamond (176 atoms/cm³). Further, amorphous diamond and diamond materials typically contract upon melting.

As used herein, “vapor deposited” refers to materials which are formed using vapor deposition techniques. “Vapor deposition” refers to a process of depositing materials on a substrate through the vapor phase. Vapor deposition processes can include any process such as, but not limited to, chemical vapor deposition (CVD) and physical vapor deposition (PVD). A wide variety of variations of each vapor deposition method can be performed by those skilled in the art. Examples of vapor deposition methods include hot filament CVD, rf-CVD, laser CVD (LCVD), laser ablation, conformal diamond coating processes, metal-organic CVD (MOCVD), sputtering, thermal evaporation PVD, ionized metal PVD (IMPVD), electron beam PVD (EBPVD), reactive PVD, atomic layer deposition (ALD), and the like.

As used herein, “electrically coupled” refers to a relationship between structures that allows electrical current to flow at least partially between them. This definition is intended to include aspects where the structures are in physical contact and those aspects where the structures are not in physical contact. Typically, two materials which are electrically coupled can have an electrical potential or actual current between the two materials. For example, two plates physically connected together by a resistor are in physical contact, and thus allow electrical current to flow between them. Conversely, two plates separated by a dielectric material are not in physical contact, but, when connected to an alternating current source, allow electrical current to flow between them by capacitive means. Moreover, depending on the insulative nature of the dielectric material, electrons may be allowed to bore through, or jump across the dielectric material when enough energy is applied.

As used herein, “adjacent” refers to near or close sufficient to achieve a desired affect.

As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result. For example, a composition that is “substantially free of” particles would either completely lack particles, or so nearly completely lack particles that the effect would be the same as if it completely lacked particles. In other words, a composition that is “substantially free of” an ingredient or element may still actually contain such item as long as there is no measurable effect on the property of interest thereof.

As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above” or “a little below” the endpoint with a degree of flexibility as would be generally recognized by those skilled in the art. Further, the term about explicitly includes the exact endpoint, unless specifically stated otherwise.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “about 1 to about 5” should be interpreted to include not only the explicitly recited values of about 1 to about 5, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc., as well as 1, 2, 3, 4, and 5, individually. This same principle applies to ranges reciting only one numerical value as a minimum or a maximum. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.

The Invention

The present disclosure provides electrode devices and systems for use in liquid environments, including associated methods. Numerous uses for such electrodes are contemplated, and any such use is considered to be within the present scope. Non-limiting examples of such uses can include ionizing a liquid, generation of hydrogen from water, generation of ozone from water, purifying a liquid, and the like.

As is shown in FIG. 1, one exemplary aspect of an electrode device for use in a liquid environment can include a proton exchange membrane (PEM) 102 having a first side 104 and a second side 106, a first electrode 108 including a carbon material, where the first electrode 108 is positioned at the first side 104 of the PEM 102. A second electrode 110 can be positioned at the second side 106 of the PEM 102 opposite the first electrode 108. The PEM 102 can function to space the first electrode 108 and the second electrode 110 at a distance of less than or equal to about 100 microns apart. In another aspect, the PEM 102 can function to space the first electrode 108 and the second electrode 110 at a distance of less than or equal to about 50 microns apart.

A PEM is a semipermeable membrane that is permeable to protons while blocking molecules such as oxygen, ozone, etc. Although any material having this semipermeable property is considered to be within the present scope, in some aspects the PEM can be made from various ionomers. As such, the PEM facilitates the separation of protons from the remaining ionized molecules of the liquid being processed. In one aspect, a PEM can be formed from a substantially pure polymer membrane. In another aspect, a PEM can be formed from composite membranes having additional materials embedded therein. Various non-limiting examples of PEMs are commercially available, such as Nafion (DuPont), which is an ionomer with a perfluorinated backbone similar to Teflon. Other examples can include polyaromatic polymers, partially fluorinated polymers, solid polymer membranes, and the like. PEMs are well known to those of ordinary skill in the art.

Various materials are contemplated for use as the first and/or second electrode. In one aspect, the first and/or second electrode can include a porous layer of DLC, a DLC-coated carbon cloth, a B-doped SiC powder, a porous layer of B-doped SiC, a B-doped SiC-coated carbon cloth, a DLC powder, and the like, including a combination thereof. In one specific aspect, the first and/or second electrode can include a DLC-coated carbon cloth. In another specific aspect, the first and/or second electrode can include a porous layer of DLC material. Any of the DLC materials utilized can be either doped or undoped. In one aspect, the DLC is doped with N. In another aspect, the DLC can be a conductive DLC material having an sp3 bonded carbon content from about 20 atom % to about 80 atom % and an sp2 bonded carbon content from about 20 atom % to about 80 atom %. In yet another aspect, at least one of the first electrode or the second electrode includes a B-doped SiC powder.

The present disclosure additionally provides systems for ionizing a liquid. In one aspect, as is shown in FIG. 2, one such system provides a liquid containment vessel 202 having a first chamber 204 and a second chamber 206, where the first chamber and the second chamber are continuous, and a PEM 208 having a first side 210 facing the first chamber 204 and a second side 212 facing the second chamber 206, where the PEM is positioned within the liquid containment vessel 202 to separate the first chamber 204 and the second chamber 206. The system can also include a first electrode 214 including a carbon material, where the first electrode 214 is positioned at the first side 210 of the PEM 208, and a second electrode 216 including a carbon material, where the second electrode 216 is positioned at the second side 212 of the PEM 208 opposite the first electrode 214. The PEM 208 spaces the first electrode 214 and the second electrode 216 at a distance sufficient to ionize the liquid. In one aspect, for example, the distance can be less than or equal to about 100 microns apart. The system additionally includes a first liquid input 218 coupled to the liquid containment vessel 202 and operable to deliver a liquid into the first chamber 204, and a first liquid output 220 coupled to the liquid containment vessel 202 and operable to remove liquid from the first chamber 204. The system can also include a second liquid input 222 coupled to the liquid containment vessel 202 and operable to deliver a liquid into the second chamber 206, and a second liquid output 224 coupled to the liquid containment vessel 202 and operable to remove liquid from the second chamber 206. The system can further include an electrical power source electrically coupled between the first electrode and the second electrode (not shown).

Thus, protons from a liquid that is ionized in the first chamber 204 can move through the PEM 208 to the second chamber 206, thus allowing the ionized liquid in the first chamber 204 to remain in an ionized state for collection and further use. In the case of water, for example, the charged electrodes can dissociate hydrogen protons from the water. These protons move across the PEM 208 and into the second chamber 206, which precludes their recombination with the dissociated oxygen from the water. In some aspects the protons can be collected for further use. The dissociated oxygen forms ozone, which can be collected via the first liquid output 220.

The present disclosure additionally provides methods for ionizing a liquid. In one aspect, relating to the system described above for example and as is shown in FIG. 3, one such method can include activating the power source to drive a current from the second electrode to the first electrode thus charging the first electrode as an anode and the second electrode as a cathode 302, delivering a working liquid through the first liquid input into the first chamber 304, and delivering a carrier liquid through the second liquid input into the second chamber 306. The method can also include ionizing the working liquid to generate protons therefrom such that the generated protons migrate across the proton exchange membrane toward the cathode and into the carrier liquid in the second chamber 308. The working liquid containing an ionized component can be removed by the first liquid output and the carrier liquid can be removed by the second liquid output. In one specific aspect, the working liquid is water and ionizing the water generates ozone at the anode. In yet another aspect, the ozone is removed from the first chamber with the water by the first liquid output.

As has been described, in one aspect an electrode can include a DLC material or an amorphous carbon material. DLC and amorphous carbon electrodes offer significant advantages over boron doped diamond electrodes, both in terms of functionality and greatly reduced manufacturing costs. It is noted that, for the present disclosure, DLC and amorphous diamond can be used interchangeably for convenience. It is important to note, however, that DLC and amorphous diamond may exhibit different functional or manufacturing characteristics, and thus can be explicitly distinguished in some cases.

Accordingly, DLC can be utilized as an electrode in a liquid environment with beneficial results. The electrode can be a substantially solid DLC material (i.e. without a support substrate) or an electrode can include a DLC layer deposited onto a substrate that provides structural support and/or electrical or semiconductive functionality. As has been described, in one aspect it can be beneficial for the DLA to be discontinuous, thus allowing a liquid to pass thereby and access the PEM associated therewith. This can be accomplished by depositing DLC onto a substrate having a porous nature. For example, DLC can be deposited onto a carbon cloth. The DLC will adhere to the fibers of the cloth, leaving at least a portion of the holes between the fibers open. This can thus allow the passage of liquid through the DLC electrode. Additionally, any substrate having holes formed therein can be utilized to a similar effect. In another aspect, the DLC layer can be deposited onto a substrate and holes be formed therein after deposition. The DLC can also be in the form of a powder or other particulate material and held in place with a confining structure that allows the flow of liquid therethrough. Similar configurations are additionally contemplated for other materials utilized to make the electrodes, such as, for example, BN. Furthermore, the DLC or the BN can be undoped or doped, as is described herein.

DLC electrodes have various superior properties compared to conventional electrodes, including metal and glassy carbon electrodes. For example, DLC is highly inert with respect to many chemical reactions. As such, a DLC electrode resists degradation even under electrolytic conditions in highly reactive liquids. Additionally, DLC electrodes appear to exhibit an over potential in water that is significantly greater than other electrodes. When water is dissociated into H+ and OH− by a cathode and an anode, H₂ will form at the cathode, and O₂ will form at the anode.

The broader working potential range in aqueous liquids also allows the production of strong oxidizing agents (e.g., hydrogen peroxide, ozone, chlorine). For example, DLC electrodes can be used to electrolytically dissociate concentrated hydro sulfuric acid (H₂SO₄) to produce peroxodisulfuric acid H₂S₂O₈, a strong oxidizing agent that is difficult if not impossible to obtain using normal metal electrodes. DLC electrodes can also be used to dissociate the molten salt of KF.2HF to produce fluorine gas. Such applications generally cannot be accomplished using conventional electrodes that lack an over potential for dissociation and the corrosion protection of DLC electrode materials.

In one aspect, DLC electrode materials can be utilized to reduce contaminants in a liquid. One example can include water purification systems. This higher current efficiency due to the over potential of the DLC electrodes allows hydroxyl radicals to be more readily formed as compared to conventional electrodes, thus more effectively removing impurities from the liquid. The polarities can be reversed to remove impurities that build up on the electrodes, thus renewing the purification system. Additionally, such systems can also eliminate bacteria, viruses, and other potentially pathogenic contaminants from a liquid.

A power source can thus be used to provide power to the first electrode and the second electrode. The power source can be any source capable of providing power to the electrodes. The power source can be AC, DC, or a combination of AC and DC such as, for example, an AC current with a DC offset, or a temporal AC and DC sequence. In one aspect, the power source charges the electrodes to a range of from about 0.5 V to about 15 V. In another aspect, the power source charges the electrodes to a range of from about 0.5 V to about 10 V. In yet another aspect, the power source charges the electrodes to a range of from about 0.5 V to about 5 V. In a further aspect, the power source charges the electrodes to a range of from about 0.5 V to about 2.5 V.

A variety of support substrate materials can be utilized in making an electrode, depending on the desired characteristics of the device. Non-limiting examples of support substrate materials include metals, metal alloys, semiconductors, ceramics, polymers, carbon materials, and the like, including combinations thereof. In another aspect, the support substrate can be a fibrous cloth, such as a carbon cloth. In some aspects, the support substrate can be a container to contain a crushed or powdered electrode material. The support substrate can also be a material that improves the adhesion of DLC thereto. One example of such a material is titanium or a titanium alloy. In one aspect, the power supply can be coupled to the support substrate. In another aspect, the power supply can be coupled to the conductive DLC or other electrode material.

Additionally, the support substrate can have a surface of any shape or configuration. DLC or other electrode materials can be coated on any shape of surface including as a conformal layer. In one aspect, the surface is planar. In another aspect, the surface can be roughened and/or corrugated. In yet another aspect, the surface can be the outside and/or the inside of a pipe or tube. For example, in one aspect a layer of DLC can be deposited on the inside surface of a tube, where the tube is thus a DLC electrode. A second electrode can be placed inside the tube and liquid can be flowed there through, thus effectively removing contaminants from the liquid as it flows continuously or non-continuously through the tube.

As one example, conductive DLC materials represent a distinct class of DLC materials having various beneficial properties, such as low resistivity, high transmissivity, etc. These properties are at least partially related to variables such as hydrogen content, sp² and sp³ bonded carbon content, and optional additives or dopants. Conductive DLC can be formed by any process capable of forming DLC having conductive properties. For example, in one aspect conductive DLC can be deposited onto a substrate using a suitable vapor deposition process. Additionally, in one specific aspect, the DLC material can be amorphous diamond.

Increased hydrogen content in the DLC material can contribute to an increase in transmissivity. If such a material is desired, the hydrogen content can be incorporated throughout the conductive DLC material or substantially only at a surface thereof. As a general guideline, in one aspect the hydrogen content can range from 0.01 atom % to about 30 atom %. In another aspect, the hydrogen content can range from about 15 atom % to about 25 atom %. In various aspects, the conductive DLC can be substantially free of hydrogen content. Hydrogen content can be increased by increasing hydrogen gas concentrations during deposition of the DLC material. Alternatively, a DLC material can be heat treated with hydrogen gas to form a hydrogen terminated surface layer of DLC. Deposition can occur using a vapor deposition process such as chemical vapor deposition, although other suitable methods can be utilized. Additionally, in some aspects a surface of the DLC material can be roughened or stippled to increase the surface area contact with the liquid.

A conductive additive or dopant can be introduced into the DLC material in some aspects to enhance or control the conductivity of the conductive DLC material. Suitable conductive additives can be incorporated via any number of approaches such as, but not limited to, codeposition in the vapor phase, coating of the conductive additives by the diamond-like carbon material, infiltration, alternating deposition of each material, and the like. Various dopants are contemplated that can be beneficial for the conductive DLC materials of the present disclosure. Non-limiting examples can include N, Si, P, Li, conductive metals, and the like, including combinations thereof. In one aspect, suitable conductive additives can include conductive metal particulates incorporated into a hydrogenated diamond-like carbon material. Non-limiting examples of metal particles include silver, copper, gold, titanium, and the like, including combinations thereof. In one specific aspect, the metal particulates can be nanoparticles, i.e. 100 nm or less and often 50 nm or less. Other metal particulates can be any suitable size, although in one aspect such particulates can be from about 1 nm to about 1 μm in size. In another aspect, metal particulates can be from about 2 nm to about 100 nm in size. In yet another aspect, metal particulates can be from about 0.1 μm to about 0.6 μm in size. Concentration of metal particulates can generally range from about 2 vol % to about 60 vol %, although optimal particle sizes and concentrations can vary considerably depending on the specific particle material, sp² and sp³ bonded carbon content, and hydrogen content. In another aspect, the conductive DLC material can be doped with nitrogen. In yet another aspect, the conductive DLC material is undoped.

Another variable with respect to the conductive DLC material is the sp³ bonded carbon content. Advantageously, an increase in sp³ bonded carbon content results in an increase in transmissivity as the diamond character of the material increase. However, this is also accompanied by an associated decrease in conductivity. Generally, the conductive DLC material can have an sp³ bonded carbon content from about 20 atom % to about 90 atom %. In another aspect, the conductive DLC material can have an sp³ bonded carbon content from about 20 atom % to about 80 atom %. In yet another aspect, the conductive DLC material can have an sp³ bonded carbon content from about 40 atom % to about 65 atom %. At higher sp³ bonded carbon contents, e.g. from about 50 atom % to about 90 atom %, additional additives and/or dopants can be introduced to increase conductivity sufficient for use of the material as a conductive electrode within the device. For example, doping with nitrogen or other similar dopants can provide good conductivity for use as a conductive DLC electrode.

sp² bonded carbon content has a graphitic form in the crystal structure of the DLC material, and is thus can be electrically conductive. As such, an appropriate balance of sp² bonded carbon content in the DLC material can be used to form a DLC electrode having good electrically conductive properties. In one aspect, the conductive DLC material can have from about 10 atom % to about 80 atom % sp² bonded carbon content. In another aspect, the conductive DLC material can have from about 20 atom % to about 80 atom % sp² bonded carbon content. In yet another aspect, the conductive DLC material can have from about 35 atom % to about 60 atom % sp² bonded carbon content. The specific content can also vary depending on hydrogen content, sp³ bonded carbon content, and other optional additives and/or dopants.

DLC materials can be made using any suitable method, such as, for example, various vapor deposition processes. In one aspect of the present disclosure, the DLC material can be formed using a cathodic arc method. Various cathodic arc processes can be utilized, such as those disclosed in U.S. Pat. Nos. 4,448,799; 4,511,593; 4,556,471; 4,620,913; 4,622,452; 5,294,322; 5,458,754; and 6,139,964, each of which is incorporated herein by reference. Generally speaking, cathodic arc techniques involve the physical vapor deposition (PVD) of carbon atoms onto a target, or substrate. The arc is generated by passing a large current through a graphite electrode that serves as an anode, and vaporizing carbon atoms with the current. If the carbon atoms contain sufficient energy (i.e. about 100 eV), they will impinge on the target and adhere to its surface to form a carbonaceous material, such as DLC or amorphous diamond. DLC material can be coated on many metallic substrates, typically with no, or substantially reduced, contact resistance. In general, the kinetic energy of the impinging carbon atoms can be adjusted by the varying the negative bias at the substrate and the deposition rate can be controlled by the arc current. Control of these parameters as well as others can also adjust the degree of distortion of the carbon atom tetrahedral coordination and the geometry, or configuration of the DLC material (i.e. for example, a high negative bias can accelerate carbon atoms and increase sp³ bonding). By measuring the Raman spectra of the material the sp³/sp² ratio can be determined. However, it should be kept in mind that the distorted tetrahedral portions of the DLC material are generally neither pure sp³ nor sp² but a range of bonds which are of intermediate character. Increasing the arc current, however, can increase the rate of target bombardment with high flux carbon ions. As a result, temperature can rise so the deposited carbon will convert to a more stable graphitic form. Thus, final configuration and composition (i.e. band gaps, NEA, and emission surface asperity) of the DLC material can be controlled by manipulating the cathodic arc conditions under which the material is formed. In some aspects, cathodic arc deposition can be utilized to form amorphous diamond materials.

Additionally, other processes can be used to form DLC such as various vapor deposition processes, e.g. chemical vapor deposition or the like. In preparing a more crystalline DLC, chemical vapor deposition can be used. Chemical vapor deposition (CVD) of diamond-like carbon can generally be performed by introducing a carbon source gas at elevated temperatures into a chamber housing a deposition substrate. If the deposition temperature is high (e.g. 800° C.), DLC will grow to as a crystalline CVD diamond film. An example of a suitable CVD process is radio frequency (13.6 MHz) CVD by dissociation of acetylene (C₂H₂) and hydrogen gas under partial vacuum (millitorr). Alternatively, pulsed DC can be used instead of RF CVD. In the case of amorphous diamond, deposition by cathodic arc or laser ablation can form a suitable layer.

The formation of the DLC material can be further facilitated through the deposition of a conformal DLC layer. Conformal diamond coating processes can provide a number of advantages over conventional diamond film processes. Conformal diamond coating can be performed on a wide variety of substrates, including non-planar substrates. A growth surface can be pretreated under diamond growth conditions in the absence of a bias to form a carbon film. The diamond growth conditions can be conditions that are conventional vapor deposition conditions for DLC without an applied bias. As a result, a thin carbon film can be formed which is typically less than about 100 angstroms. The pretreatment step can be performed at almost any growth temperature such as from about 200° C. to about 900° C., although lower temperatures below about 500° C. may be particularly useful. Without being bound to any particular theory, the thin carbon film appears to form within a short time, e.g., less than one hour, and is a hydrogen terminated amorphous carbon.

Following formation of the thin carbon film, the growth surface can then be subjected to diamond growth conditions to form the DLC layer. The diamond growth conditions can be those conditions which are commonly used in traditional vapor deposition diamond growth. However, unlike conventional DLC layer growth, a DLC layer produced using the above pretreatment steps results in a conformal DLC layer that typically begins growth substantially over the entire growth surface with substantially no incubation time.

One aspect of the DLC material that facilitates electrical conductivity is the distorted tetrahedral coordination with which many of the carbon atoms are bonded. Tetrahedral coordination allows carbon atoms to retain the sp³ bonding characteristic that provides a plurality of effective band gaps, due to the differing bond lengths of the carbon atom bonds in the distorted tetrahedral configuration. DLC materials having varying degrees of electrical conductivity are contemplated. It is noted that the electrical conductivities of the DLC materials of the present disclosure have been expressed in terms of resistivity. In one aspect, for example, the conductive DLC material can have a resistivity from about 0 μΩ-cm to about 80 μΩ-cm at 20° C. such that the material is electrically conductive. In another aspect, the resistivity of the conductive DLC material can be from about 0 μΩ-cm to about 40 μΩ-cm.

Additionally, excessive grain boundaries within the conductive DLC material can increase the resistivity of the material. Grain boundaries can be minimized using a variety of techniques. In one approach, for example, formation of the DLC material can be initiated using nanodiamond seeding. Another approach can include the high temperature annealing of the DLC material to reduce grain boundaries. Further, it can be beneficial to have a DLC surface roughness that is less than about 30 nm. A variety of techniques can be utilized to produce such a smooth surface such as, for example, reverse casting using a smooth inverse mold, polishing, or other similar processes. In another approach, a support substrate can be prepared by etching to roughen the support substrate surface upon which the DLC will be deposited. Such a roughened surface can enhance DLC grain growth and further increase electron flow into the DLC material during growth.

The conductive DLC material can have any functional thickness. In some aspects, for example, the DLC electrode is made completely from or substantially completely from DLC material. As such, the DLC material in this case can be as thick as or thicker than what is required for the DLC electrode to support itself. In other aspects, the DLC material is supported by a support substrate and can be thick enough to facilitate the electrical conductivity required to perform the function of the DLC electrode device. In one specific aspect, the DLC material can have a thickness of from about 0.01 μm to about 10 μm. In another aspect, the DLC material can be from about 1 μm to about 50 μm. In yet another aspect, the DLC material can be from about 50 μm to about 100 μm.

Of course, it is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention and the appended claims are intended to cover such modifications and arrangements. Thus, while the present invention has been described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred embodiments of the invention, it will be apparent to those of ordinary skill in the art that numerous modifications, including, but not limited to, variations in size, materials, shape, form, function and manner of operation, assembly and use may be made without departing from the principles and concepts set forth herein. 

What is claimed is:
 1. An electrode device for use in a liquid environment, comprising: a proton exchange membrane having a first side and a second side; a first electrode including a carbon material, the first electrode positioned at the first side of the proton exchange membrane; a second electrode positioned at the second side of the proton exchange membrane opposite the first electrode, wherein the proton exchange membrane spaces the first electrode and the second electrode at a distance of less than or equal to about 100 microns apart.
 2. The device of claim 1, wherein the wherein the proton exchange membrane spaces the first electrode and the second electrode at a distance of less than or equal to about 50 microns apart.
 3. The device of claim 1, wherein the first electrode includes a member selected from the group consisting of a porous layer of DLC, a DLC-coated carbon cloth, a B-doped SiC powder, a porous layer of B-doped SiC, a B-doped SiC-coated carbon cloth, or a combination thereof.
 4. The device of claim 1, wherein the first electrode is a DLC-coated carbon cloth, wherein the DLC is doped with N.
 5. The device of claim 1, wherein the first electrode includes a porous layer of conductive DLC material with an sp3 bonded carbon content from about 20 atom % to about 80 atom % and an sp2 bonded carbon content from about 20 atom % to about 80 atom %.
 6. The device of claim 1, wherein the second electrode includes a carbon material selected from the group consisting of a porous layer of DLC, a DLC-coated carbon cloth, a B-doped SiC powder, a porous layer of B-doped SiC, a B-doped SiC-coated carbon cloth, or a combination thereof.
 7. The device of claim 1, wherein the second electrode is a DLC-coated carbon cloth, wherein the DLC is doped with N.
 8. The device of claim 1, wherein the second electrode includes a porous layer of conductive DLC material with an sp3 bonded carbon content from about 20 atom % to about 80 atom % and an sp2 bonded carbon content from about 20 atom % to about 80 atom %.
 9. The device of claim 1, wherein at least one of the first electrode or the second electrode includes a B-doped SiC powder.
 10. The device of claim 1, wherein the first electrode and the second electrode directly contact the proton exchange membrane.
 11. A system for ionizing a liquid, comprising: a liquid containment vessel having a first chamber and a second chamber, the first chamber and the second chamber being continuous; a proton exchange membrane having a first side facing the first chamber and a second side facing the second chamber, the proton exchange membrane positioned within the liquid containment vessel to separate the first chamber and the second chamber; a first electrode including a carbon material, the first electrode positioned at the first side of the proton exchange membrane; a second electrode, the second electrode positioned at the second side of the proton exchange membrane opposite the first electrode, wherein the proton exchange membrane spaces the first electrode and the second electrode at a distance of less than or equal to about 100 microns apart; a first liquid input coupled to the liquid containment vessel and operable to deliver a liquid into the first chamber; a first liquid output coupled to the liquid containment vessel and operable to remove liquid from the first chamber; a second liquid input coupled to the liquid containment vessel and operable to deliver a liquid into the second chamber; and a second liquid output coupled to the liquid containment vessel and operable to remove liquid from the second chamber.
 12. The system of claim 11, further comprising an electrical power source electrically coupled between the first electrode and the second electrode.
 13. The system of claim 11, wherein the wherein the proton exchange membrane spaces the first electrode and the second electrode at a distance of less than or equal to about 50 microns apart.
 14. The system of claim 11, wherein the first electrode includes a member selected from the group consisting of a porous layer of DLC, a DLC-coated carbon cloth, a B-doped SiC powder, a porous layer of B-doped SiC, a B-doped SiC-coated carbon cloth, or a combination thereof.
 15. The system of claim 11, wherein the second electrode includes a member selected from the group consisting of a porous layer of DLC, a DLC-coated carbon cloth, a B-doped SiC powder, a porous layer of B-doped SiC, a B-doped SiC-coated carbon cloth, or a combination thereof.
 16. A method for ionizing a liquid using the system of claim 12, comprising: activating the power source to drive a current from the second electrode to the first electrode thus charging the first electrode as an anode and the second electrode as a cathode; delivering a working liquid through the first liquid input into the first chamber; delivering a carrier liquid through the second liquid input into the second chamber; ionizing the working liquid to generate protons therefrom such that the generated protons migrate across the proton exchange membrane toward the cathode and into the carrier liquid in the second chamber; and removing the carrier liquid from the second liquid output.
 17. The method of claim 16, wherein the working liquid is water and ionizing the water generates ozone at the anode.
 18. The method of claim 17, wherein the ozone is removed from the first chamber with the water by the first liquid output. 